Electrophotographic image forming apparatuses are widely prevalent. It is because high-quality images can be obtained within a short time in comparison with image forming apparatuses of other systems such as the inkjet system.
In an electrophotographic image forming apparatus, an image is formed on a medium such as paper using an image forming developer. In this image forming process, after the image forming developer adheres to an electrostatic latent image formed on the surface of a photosensitive drum, the image forming developer is transferred to the surface of the medium.
Concerning this electrophotographic image forming apparatus, various investigations have been made. Specifically, in order to form an image structure that can conceal internal information, a bonding developer is used together with the image forming developers (for example, see Patent Document 1).
In forming this image structure, after an image is formed on the surface of the medium using the image forming developers, the medium on which the image is already formed that is folded in two is bonded so as to conceal the internal information (image) using the bonding developer. In this image structure, because the bonded medium can be peeled off, the concealed internal information can be read as necessary.